Tomographic imaging is a signal acquisition and processing technology that allows for high-resolution cross-sectional imaging in biological systems. Tomographic imaging systems include, for example, optical coherence tomography systems, ultrasound imaging systems, and computed tomography. Tomographic imaging is particularly well-suited for imaging the subsurface of a vessel or lumen within the body, such as a blood vessel, using probes disposed within a catheter through a minimally invasive procedure.
Typical tomographic imaging catheters consist of an imaging core that rotates and moves longitudinally through a blood vessel, while recording an image video loop of the vessel. The motion results in a 3D dataset, where each frame provides a 360 degree slice of the vessel at different longitudinal section. These frames provide cardiologists with invaluable information such as the location and severity of the stenosis in a patient, the presence of vulnerable plagues, and changes in the disease over time. The information also assists in determining the appropriate treatment plan for the patient, such as drug therapy, stent placement, angioplasty, or bypass surgery.
One of the most common analyses performed is the placement and apposition of stents. A stent is a small, typically meshed or slotted, tube-like structure made of a metal or polymer that is inserted into the blood vessel to hold vessel open and keep it from occluding and provides a framework for arterial lesions that are likely to embolize after balloon angioplasty. During placement, the stent should be placed in parallel within the vessel and contact the vessel wall. Apposition of a coronary artery stent is the term for how well stent lies against the wall of the artery. When the stent as placed does not mesh completely against the blood vessel, the stent is in ‘incomplete apposition’. Incomplete apposition may raise the risk of a subsequent blockage or thrombus because of blood pooling or stagnating in the dead space between the stent and the coronary artery wall. Therefore, it is critical to verify that the stent is properly employed.
In order to identify and measure stent opposition in intravascular images, a cardiologist typically has to manually locate the stent struts, which are the framework of the stent visible in the tomographic image. Generally, identification of at least two stent struts is required to determine stent apposition. This process can be a very time consuming and is prone to user error.